Waveguide power limiter comprising a longitudinal arrangement of alternate ferrite rods and dielectric spacers

ABSTRACT

A microwave power limiter having a plurality of spaced, uniformly dimensioned ferrite rods aligned along and adjacent to the side or narrow wall of a rectangular waveguide propagating the energy to be limited. The ferrite rods are separated by dielectric rods which are identical in configuration to the ferrite rods and are characterized by the same dielectric constant. A magnetic bias is applied parallel to the side or narrow waveguide wall in the vicinity of the laminated ferrite and dielectric rod structure to provide a condition of subsidiary resonance.

United States Patent 2,958,055 10/1960 Rowen 333/81 B 2,981,907 4/1961 Bundy 333/81 B 3,063,028 11/1962 Weiss 333/242 3,128,439 4/1964 Brown et al. 333/242 3,131,366 4/1964 Dixon 333/242 3,316,508 4/1967 Jones et a1. 333/242 3,500,256 3/1970 Carter et al 333/17 Primary Examiner-Herman Karl Saalbach Assistant Examiner-Paul L. Gensler Attorneys-Harry M. Saragovitz, Edward J. Kelly, Herbert Berl and Jack 11. Stanley [72] Inventors John L. Carter Oakhurst; Joseph W. McGowan, Spring Lake Heights, both of NJ. [21] Appl. No. 862,734 [22] Filed Oct. 1, 1969 [45] Patented Dec. 21, 19711 [73] Assignee The United States 01 America as represented by the Secretary of the Army [54] WAVEGUIDE POWER LIMITER COMPRISING A LONGI'IUDINAL ARRANGEMENT 0F ALTERNATE FERRITE RODS AND DIELECTRIC SPACERS 8 Claims, 5 Drawing Figs.

'[52] U.S.Cl 333/117, 333/242 [51] Int. Cl ..1-l03g11/04, 1101p 1/32 [50] Field of Search 333/242, 17,81,81B,24.1,73 W

[56] References Cited 7 UNITED STATES PATENTS 2,883,629 4/1959 Suhl 333/24.2X

ION

lNPUT l I? l us INSERTION LOSS (db) I F l I l I I l l J 01000? 9.5 8.6 0.7 8.8 9.9 9.0 9.1 9.2 9.3 9.4 9.5

FREQUENCY (011 1,000 FIG. 2

1. D O. S O '0' POWER INPUT(WATTS) FIG.

$8 05 Z J Q 1 1 1 1 1 1 1 1 1 1 8.5 8.6 8.7 9.9 9.9 9. 9.1 9.2 9.3 9.4 9.5 :1 FREQUENCY (011 FIG. 4 3 ,100-

5- D O. '5 o 10 INVENTORS. 0: JOHN L. CARTER & 2, JOSEPH w. meow/11v 0 BY; I 1 1 1 1 %AGENT 10 100 1,000 10,000 flu; J 1 I POWER INPUT(WATTS) 910/ FIG. 5

ATTORNEYS.

BACKGROUND OF THE INVENTION This invention relates to waveguide transmission systems utilizing gyromagnetic elements and more particularly to gyromagnetic elements for use in such systems as power limiters.

It is well known that gyromagnetic mediums such as ferrites are characterized by certain unpaired electron spins which respond to a transmitted microwave signal by precessing gyroscopically about the line of an applied magnetic field. When the frequency of the applied signal is equal to the natural precession frequency of the electron spins, a resonant condition exists under which the electron spins are able to absorb large amounts of energy. from the signal and thereby greatly attenuate the signal. Assuming a given condition of subsidiary resonance at a DC magnetic field H, it is characteristic of such ferrites that the signal attenuation is very low below a critical power level P but beyond this point the attenuation increases linearly due to the resonance effects. As a result, the power output remains substantially constant for input power levels beyond the critical power level P Power limiting is thereby achieved. However, when such power limiting devices were used in duplexing systems for crystal protection in radar system receivers, the threshold or critical power level for limiting was found to be too high for adequate protection. It is also well known that by utilizing a slab of ferrite and an adjacent dielectric slab along a sidewall of a waveguide, and applying an appropriate subsidiary resonance DC magnetic field in a direction transverse to the direction of the RF magnetic field, H the RF magnetic field in the ferrite may be increased and thus lower the threshold or critical power level. The interaction between the RF magnetic field and the DC magnetic field is a function of the sine of the angle between H and the DC magnetic field. However, the threshold or critical level still proved to be too high for use in duplexing waveguide systems for proper crystal protection. It was also found that the operational frequency of such a device was rather limited inasmuch as it led to separate high-absorption loss peaking at relatively low-power levels. Such peaks restrict the operational frequency bandwidth since the only useable frequency is intermediate the high-absorption loss peaks.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a ferrite power limiter for operation at microwave frequencies wherein the aforementioned limitations are overcome.

It is another object of the present invention to provide a ferrite power limiter wherein an optimum ratio of low-level insertion loss to high-level insertion loss is achieved over a wide frequency range.

In accordance with the present invention there is provided a device for limiting the power level of microwave energy. Included is a rectangular waveguide section having wide top and bottom walls and relatively narrow sidewalls, and further including a plurality of uniformly spaced, identical rectangular ferrite rods, each of which are square in cross section, posi' tioned in the waveguide section adjacent the inner surface of one of the narrow sidewalls with their axes normal to the wide top and bottom walls. The width of the ferrite rods is smaller than the guide wavelength and is much smaller than the axial dimension thereof. The ferrite rods are separated by dielectric rods which are identical in configuration to the ferrite rods and also have the same dielectric constant. Also included are means for magnetically biasing the ferrite rods in a plane parallel to the narrow sidewall along which the spaced ferrite rods are aligned in a row' to produce subsidiary resonance excitation therein.

BRIEF DESCRIPTION OF THE DRAWING For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawing in which:

FIG. 1 illustrates a preferred embodiment of and FIGS. 2-5 are explanatory curves.

the invention;

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. I, at 10 there is shown a rectangular waveguide section adapted to propagate microwave energy in the conventional-TE mode. Positioned within waveguide section 10 longitudinally along and adjacent one narrow wall 12 are a plurality of spaced, uniform ferrite rods 14 which extend from the bottom waveguide surface 16 to top waveguide surface 18. Each of the ferrite rods 14 are rectangular, and of square cross section, and the width dimension is small in comparison to the axial dimension thereof. The cross-sectional dimension of ferrite rods 14, i.e., depth or width, is such that this dimension is substantially one-thirtieth of the guide 10 wavelength.

As shown, the ferrite rods M are separated by discrete dielectric rods 20, each of which have the exact same dimensions and dielectric constant as each of the ferrite rods 14. The dielectric rods 20 provide magnetic insulation between each ferrite rod. In effect, the rods 14 and 20 form an integrated laminated structure. A DC magnetic field H is applied in the direction of the arrow 22 parallel to narrow waveguide wall 12 by any suitable means well known in the art. The magnitude of H, is such as to produce subsidiary resonance excitation in ferrite rods 20.

The operation of FIG. 1 as a power limiter is based on the fact that each of the ferrite rods can be considered to be similar to the idealized needlelike configuration for achieving the lowest threshold value. This value is achieved where the demagnitizing factors N N and N have values of 0, 0.5 and 0.5 respectively. N is along the longitudinal dimension of the ferrite rods 20 and is in the direction of the applied DC magnetic biasing field H,,.

It is to be understood of course that this invention is not to be limited to ferrite elements and dielectric spacer elements of square cross section, but that elements of circular cross section could also be utilized to achieve the same result.

In one preferred embodiment, the laminated structure comprised six spaced polycrystalline YIG rods for operation at X- band. The YIG rods and the dielectric rod spacers were each 0.110 inch X 0.110 inch 0.398 inch. FIG. 2 shows the lowlevel insertion loss as a function of frequency for this embodiment and FIG. 3 shows the power-limiting action of the structure. In FIG. 3, the threshold or critical power level is 20 watts and the dynamic range is about 23 db.

In another embodiment of the invention for operation at X- band, the laminated structure comprised six spaced polycrystalline YIG rods followed by fiwe spaced single crystal YIG rods. As in the previous embodiment, all the YIG rods and the dielectric spacers therebetween were each 0.1 10 inch X 0.1 10 inch X0398 inch. FIG. 4 shows. the low-level insertion loss as a function of frequency for this embodiment and FIG. 5 shows the power-limiting action of the structure. As can be seen, the threshold or critical power level is about 2.8 watts and the dynamic range is about 30 db.

We wish it to be understood that we do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art. I

What is claimed is:

I. A device for limiting the power level of microwave energy comprising:

a rectangular waveguide section having opposed wide walls and opposed narrow walls,

a plurality of elongated rectangular ferrite rods positioned within said waveguide section and with their axes normal to the opposed wide walls and uniformly spaced in a row longitudinally along and adjacent one of the narrow walls,

the longest dimension of each of said ferrite rods being the axial dimension,

and means for magnetically biasing said ferrite rods in a plane parallel to said one narrow wall to produce subsidiary resonance excitation in said ferrite elements.

2. The device in accordance with claim 1 wherein said ferrite rods are of identical configuration and square in cross section.

3. The device in accordance with claim 2 wherein the ratio of the width of said ferrite rods to the guide wavelength is substantially one to 30.

4. The device in accordance with claim 1 and further including discrete-elongated dielectric spacers between each pair of said ferrite rods.

5. The device in accordance with claim 4 wherein said dielectric spacers and said ferrite rods are characterized by identical dielectric constants.

6. The device in accordance with claim 5 wherein the ratio of the width of said ferrite rods to the guide wavelength is substantially one to 30.

7. The device in accordance with claim 2 and further including discrete dielectric rods between each pair of said ferrite rods, said dielectric rods being identical in configuration to said ferrite rods.

8. The device in accordance with claim 7 wherein said dielectric rods and said ferrite rods are characterized by identical dielectric constants. 

1. A device for limiting the power level of microwave energy comprising: a rectangular waveguide section having opposed wide walls and opposed narrow walls, a plurality of elongated rectangular ferrite rods positioned within said waveguide section and with their axes normal to the opposed wide walls and uniformly spaced in a row longitudinally along and adjacent one of the narrow walls, the longest dimension of each of said ferrite rods being the axial dimension, and means for magnetically biasing said ferrite rods in a plane parallel to said one narrow wall to produce subsidiary resonance excitation in said ferrite elements.
 2. The device in accordance with claim 1 wherein said ferrite rods are of identical configuration and square in cross section.
 3. The device in accordance with claim 2 wherein the ratio of the width of said ferrite rods to the guide wavelength is substantially one to
 30. 4. The device in accordance with claim 1 and further including discrete-elongated dielectric spacers between each pair of said ferrite rods.
 5. The device in accordance with claim 4 wherein said dielectric spacers and said ferrite rods are characterized by identical dielectric constants.
 6. The device in accordance with claim 5 wherein the ratio of the width of said ferrite rods to the guide wavelength is substantially one to
 30. 7. The device in accordance with claim 2 and further including discrete dielectric rods between each pair of said ferrite rods, said dielectric rods being identical in configuration to said ferrite rods.
 8. The device in accordance with claim 7 wherein said dielectric rods and said ferrite rods are characterized by identical dielectric constants. 